1. Field of the Invention
The present invention relates generally to devices for extrusion, and in particular, to a device for continuous extrusion without reverse flow of compounded rubber during which impurities are removed by a vacuum removal process.
2. Description of the Prior Art
Prior art devices for extruding material, especially rubber, include various cylindrical and conical helix screw feed mechanisms for moving the material through a barrel and liner. Many of these extrusion devices include means for drawing off impurities during processing, such as by vacuum. A problem typical of cylindrical helix- or screw-type extrusion devices is that the material head pressure may become so great that the rubber is forced in a direction opposite the desired direction of flow. The resulting regurgitation or reverse flow is especially troublesome in both vacuum and nonvacuum type extruders, since the rubber may be eventually forced back into either the vacuum or the feed section of the device, thereby causing the vacuum port and feed section mechanisms to become obstructed. When this occurs, the equipment must be shut down with concomitant lost production time and increased costs.
To compound this problem, the outer edges of the fluted screw helix as well as the walls of the barrel liner in cylindrical-type prior art devices tend to become badly worn in time, further increasing the possibility of unwanted regurgitation or reverse flow. Thus, frequent replacement of worn barrel, liner and screw members is required to insure against regurgitation resulting in increased and costly delays in production and overall operational inefficiency. In addition, conventional cylindrical screw devices require a screw of substantial length having many threads in order to minimize the chance of regurgitation.